Natural and synthetic clays having lamellar structures with interlamellar spaces disposed between the lamellar layers are well known. Smectites, such as bentonite, montmorillonites and the like are a class of clays possessing such a lamellar structure. Montmorillonite has an idealized stoichiometric composition corresponding to Na.sub.0.67 Al.sub.3.33 Mg.sub.0.67 (Si.sub.8)O.sub.20 (OH).sub.4. Structurally, it comprises a central layer containing octrahedrally coordinated aluminum and magnesium in the form of their oxides and hydroxides sandwiched between two layers containing tetrahedrally coordinated silicon essentially in the form of its oxide. Normally in nature cations are present to compensate for the charge imbalance caused by isomorphous substitution of Mg.sup.2+ for Al.sup.3+ in the octahedral layer, and/or Al.sup.3+ or other ions for Si.sup.4+ in the tetrahedral layers. The octrahedral and tetrahedral regions are tightly bound together to form a lamellar layer. The space between these lamellar layers, i.e., the interlamellar space, in natural clays is normally occupied by exchangeable Ca.sup.2+ or Na.sup.+ ions. The distance between the interlamellar layers can be substantially increased by absorption of a variety of polar molecules such as water, ethylene glycol, amines, etc., which enter the interlamellar space and in doing so push apart the lamellar layers. The interlamellar spaces tend to collapse when the molecules occupying the space are removed, for example by heating the clay at a high temperature.
U.S. Pat. Nos. 4,216,188 and 4,248,739 disclose stabilized pillared interlayered clays in which the layers are separated and supported by "pillars" of oligomeric or polymeric species derived from metal hydroxides. In U.S. Pat. No. 4,248,739 the use of the pillared interlayered clays as sorbents, catalysts and catalytic supports is described.
Alkylation is a reaction in which an alkyl group is added to an organic molecule. The reaction of an isoparaffin with an olefin to provide an isoparaffin of higher molecular weight is an example of such a reaction. The reaction of C.sub.2 to C.sub.5 olefins with isobutane in the presence of an acidic catalyst to produce so-called "alkylates" has resulted in the manufacture of valuable blending components for gasoline, due to the fact that these alkylates have high octane ratings.
Traditionally, industrial alkylation processes for making isoparaffin-olefin alkylates include the use of hydrofluoric acid or sulfuric acid as catalysts under controlled temperature conditions. Low temperatures are utilized in the sulfuric acid process to minimize the side reaction of olefin polymerization, and the acid strength is generally maintained at 88 to 94% by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature-sensitive and the acid is easily recovered and purified. These processes have inherent drawbacks including environmental concerns, acid consumption and sludge disposal as well as problems relating to the handling and disposal of corrosive materials.
Substantial efforts have been made to develop commercially acceptable isoparaffin-olefin alkylation processes using solid catalysts. A wide variety of materials have been examined as potential catalysts for these processes, including ion-exchange resins and zeolites. Alone, both the ion-exchange resins and zeolites have low activity and deactivate rapidly. However, the addition of Lewis acids, such as BF.sub.3, to these materials enhance both activity and selectivity. Clays, such as montmorillonite, have been shown to possess the ability to promote organic reactions as acid catalysts. However, they have been superseded by other materials such as zeolites because of their lack of thermal stability at higher temperatures.
With the increasing demands for higher octane gasolines and the increasing environmental concerns, it would be advantageous to develop an isoparaffin-olefin alkylation process based on a solid catalyst. The treated pillared clay catalysts of the present invention offer refiners a more environmentally acceptable isoparaffin-olefin alkylation process than the currently used hydrofluoric and sulfuric acid alkylation processes.